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[No. 19] The number of poles in a rotary electrical machine
The figure shows the some of the effects of polenumber on the magnetic field in a rotary electrical machine. It is a highly idealised figure: the winding is a currentsheet in th…

[No. 18] Is it time to celebrate?
In Finite Elements in Electrical and Magnetic Field Problems, edited by M.V.K. Chari and P.P. Silvester, (Wiley, 1980, ISBN 0 471 27578 6), A.L. Frisiani, G. Molinari and A. Vivia…

[No. 17] Classification of electric machines
The diagram shows most of the electric machines in common use, together with the two reluctance machines which are rare but interesting. Classification is much more than an acade…

[No. 16] Four rules of saliency
We often hear the terms "salientpole" or "nonsalientpole" in relation to electric machines. "Saliency" is the idea of "projecting beyond the general outline", and it refers to…

[No. 15] Reading a winding diagram
Winding diagrams come in many different formats. There is no universal standard, but several common conventions can be found in the winding diagrams used by different manufacturin…

[No. 14] Synthesis of AC motor windings
How should we synthesize a suitable winding layout for an AC brushless PM motor? While the properties of existing windings can easily be analysed using a spreadsheet program, it …

[No. 13] Winding diagram for an AC motor
Here we see a winding diagram for a 3phase AC induction motor or brushless PM motor (IPM), having 4 poles and 36 slots. This winding could in fact be used with any AC machine, i…

[No. 12] The IPM
The IPM or interior permanentmagnet motor started its history as a linestart motor in the 1950s. At that time Alnico magnets were the best available, but their low coercivity me…

[No. 11] What is the finiteelement method?
The idea in the finiteelement method is to divide a difficult problem into a number of simpler problems which can be solved simultaneously; the solution to the difficult problem…

[No. 10] RW
All electric machines use wire — usually of copper, but sometimes of aluminium. The electrical resistance R determines the I2Rloss (Joule loss) in each winding when the RMS curre…

[No. 9] Can a magnetic circuit work without air ?
Recently the U.K. Magnetics Society sent a list of 10 questions for their magazine MagNews, in which the first question was “What is your favourite magnetic material?” In a hurry…

[No. 8] Hysteresis
At the JMAG Users’ Conference in Strasbourg last October, Hiroyuki Sano (JSOL) and Yves Thiolière (Powersys) gave a detailed class tutorial on the hysteron, a defined trapezoidal …

[No. 7] Peripheral, marginal, secondorder, inexact . . . and IMPORTANT!
The finiteelement method is very rarely exactly correct. Now surely that is an outrageous thing to say on the JMAG website! But what do we mean by exactly? The finiteelement met…

[No. 6] The Periodic Table of Electric Machines
When the archaeologists dig us up in 5,000 years’ time, they will find a large number of electric motors and generators. Who knows if they will understand what they find? They w…

[No. 5] Formulas and Equations
What’s the difference between a formula and an equation? Take the examples,

[No. 4] The Historic ClawPole Machine
My grandson is interested in mathematics and history. Maybe it is an unusual combination, but both these subjects are helpful in looking forwards as well as backwards. In engineer…